This invention relates generally to elastomeric grommets and more specifically to elastomeric grommets having a head at one end which is forced through a panel hole to mount the elastomeric grommet to the panel for passing a component through the panel hole.
Such grommets are disclosed for example in U.S. Pat. No. 2,705,308 issued to Forbes Howard Mar. 29, 1955 and in U.S. Pat. No. 4,675,937 issued to Seiji Mitomi June 30, 1987.
These grommets which are typical of prior art grommets are pushed axially into the panel hole until the panel is trapped between a head at one end of the grommet and a shoulder which is spaced rearwardly of the head. During this panel mounting procedure, the head is first compressed radially inwardly to fit through the panel hole and then expands radially outwardly after passing through the panel hole to engage the backside of the panel so as to retain the grommet against pull out. The head and shoulder also typically clamp the grommet in place on the panel.
The grommets exemplified by the U.S. Patents noted above typically have relatively high engage force requirements primarily due to the need to compress the head of the grommet as it is pushed through the panel hole. The need for a strong clamping force may also contribute significantly to the relatively high engagement force requirement. In addition these typical prior art grommets often do not have a very high retention force primarily because the retention force depends on expansion of the head and is therefore substantially related to engage force requirements. In other words, reduced engage force requirements are typically accompanied by a reduced retention force and vice-versa.